Automatic probe ground connection checking techniques

ABSTRACT

A test system can include a probe suitable to be coupled between a test measurement device and a device under test (DUT). The probe can include a signal input to receive an active signal from the DUT and a signal output to provide the active signal to the test measurement device. The probe can also include an input ground to connect to the DUT ground and an output ground to connect to the test measurement device ground. A probe ground connection checking device can automatically determine whether the probe ground connections to the DUT ground and test measurement device ground are solid.

BACKGROUND OF THE INVENTION

The connection between an oscilloscope probe and a device under test(DUT) is often unreliable due to motion of the probe, e.g., if held byhand, motion of the DUT, e.g., vibration or thermal expansion, or both.The presence of a faulty connection for the “active” lead, e.g., signallead of a probe to the DUT, is usually easy to determine if theregistered signal is dramatically different from the expected signal.

However, the presence of a faulty connection for the “cold” lead, e.g.,ground lead of a probe or negative lead of a differential probeconnected to the DUT ground, is much more difficult to determine This isbecause there is usually a low-frequency ground connection between theoscilloscope and the DUT through grounding power cords, other probechannel grounds, etc., and sometimes a high-frequency connection throughcapacitive coupling across the faulty connection. Thus, only a band offrequencies is typically misrepresented in the acquired oscilloscoperecord, which often causes subtle errors that are easy to miss by auser.

Oscilloscope users have traditionally dealt with this unreliability byeither wiggling the probe to see if anything changes in the signal ortemporarily disconnecting the probe from the oscilloscope and measuringthe resistance from the probe ground to the DUT ground with an ohmmeter.

While the “probe wiggling” approach is generally quick and intuitive,this approach is rather heuristic in nature and often causes a goodconnection to become bad. While the “temporary disconnecting” approachindeed checks the probe ground to DUT ground connection, this approachrequires manual intervention and also adds wear to the probe connector.

SUMMARY OF THE INVENTION

Embodiments of the disclosed technology generally include an automatedprobe-to-DUT (device under test) connection verification that can beeasily initiated through an oscilloscope user interface, e.g., by way ofa button on the probe or oscilloscope front-panel, a menu entry, aremote command over a general purpose interface bus (GPIB) or local areanetwork (LAN), automatically, or any combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a testing system in accordance withcertain embodiments of the disclosed technology.

FIG. 2 illustrates an example of a first technique for checking a groundconnection between an oscilloscope and a DUT, such as the oscilloscopeand DUT of FIG. 1, in accordance with certain embodiments of thedisclosed technology.

FIG. 3 illustrates an example of a second technique for checking aground connection between an oscilloscope and a DUT, such as theoscilloscope and DUT of FIG. 1, in accordance with certain embodimentsof the disclosed technology.

FIG. 4 illustrates an example of a third technique for checking a groundconnection between an oscilloscope and a DUT, such as the oscilloscopeand DUT of FIG. 1, in accordance with certain embodiments of thedisclosed technology.

FIG. 5 illustrates an example of a fourth technique for checking aground connection between an oscilloscope and a DUT in accordance withcertain embodiments of the disclosed technology.

FIG. 6 illustrates an example of a fifth technique for checking a groundconnection between an oscilloscope and a DUT in accordance with certainembodiments of the disclosed technology.

FIG. 7 illustrates an example of a sixth technique for checking a groundconnection between an oscilloscope and a DUT, such as the oscilloscopeand DUT of FIG. 1, in accordance with certain embodiments of thedisclosed technology.

DETAILED DESCRIPTION

Embodiments of the disclosed technology generally include varioustechniques for automatically checking a ground connection between anoscilloscope and a device under test (DUT), e.g., within a probe and/orprobe cable. These and other features and embodiments of the presentinvention proceed with reference to each of the figures.

FIG. 1 illustrates an example of a testing system 100 in accordance withcertain embodiments of the disclosed technology. The testing system 100includes an oscilloscope 102, a DUT 104, and a ground connection 106between the oscilloscope 102 and the DUT 104. The ground connection 106is usually established by way of a probe and corresponding probe cableand/or other suitable connecting mechanism.

The testing system 100 also includes an auxiliary ground 108 that existsdue to indirect physical connections between the oscilloscope 102 andthe DUT 104, such as power-cord ground connections, ground connectionsof other probes, a table or other supporting structure, floor, etc. Incertain systems, however, the auxiliary ground 108 is not present.

FIG. 2 illustrates an example of a first technique 200 for checking aground connection between an oscilloscope and a DUT, such as theoscilloscope 102 and the DUT 104 of FIG. 1, in accordance with certainembodiments of the disclosed technology. The example includes a probe orprobe cable 202, such as a coaxial cable, that has a signal input 204 a,e.g., to receive an active signal from the DUT, a signal output 204 b,e.g., to provide the signal to the oscilloscope, an input ground 206 a,e.g., to connect to the DUT ground, and an output ground 206 b, e.g., toconnect to the oscilloscope ground.

In the example, the first technique 200 includes the inductive couplingof a test coil 208 to the probe cable 202 by passing both through amagnetic core 210 and measuring the inductance of the test coil 208,e.g., by way of an optional impedance meter 212. This may be performed,for example, by injecting an alternating current therein and measuringthe resulting voltage.

A solid probe-to-DUT ground connection, combined with anotheroscilloscope-to-DUT ground connection, e.g., power cords, may create ashorted loop through the magnetic core, thereby lowering the inductanceof the test coil.

One having ordinary skill in the art will appreciate that theillustrated technique 200 is shown functionally and that the physicalimplementation thereof may be accomplished using any of a number ofways. For example, either or both of the test coil 208 and magnetic core210 may be partially or fully integrated with the probe cable 202 or,alternatively, removably attachable thereto. Similarly, the optionalimpedance meter 212 or other suitable measurement device may beintegrated with or separate from either or both of the test coil 208 andmagnetic core 210.

The illustrated technique 200 provides a number of advantages. Forexample, the magnetic core 210, test coil 208, or combination thereofare generally easy to add to existing probe designs. Alternatively, themagnetic core 210, test coil 208, or combination thereof may beconstructed as a separate accessory that may be used in connection withvirtually any existing probe cable.

The illustrated technique 200 is also advantageous in that suchimplementations generally do not interfere with the signal-path designof a probe. Further, verification of the ground connection may beperformed without affecting active signal acquisitions, at least insituations where the connection is solid.

FIG. 3 illustrates an example of a second technique 300 for checking aground connection between an oscilloscope and a DUT, such as theoscilloscope 102 and the DUT 104 of FIG. 1, in accordance with certainembodiments of the disclosed technology. The example includes a probe orprobe cable 302 that has a signal input 304 a, e.g., to receive anactive signal from the DUT, a signal output 304 b, e.g., to provide thesignal to the oscilloscope, an input ground 306 a, e.g., to connect tothe DUT ground, and an output ground 306 b, e.g., to connect to theoscilloscope ground.

In the example, the technique 300 includes separating the input ground306 a from the output ground 306 b, e.g., by way of a switch mechanism308, inserting a direct current into the input ground 306 a, andchecking for a low DC resistance return path, e.g., through theprobe-to-DUT ground connection and oscilloscope-to-DUT groundconnection. The determination of a low DC resistance return path mayindicate that the ground path within the probe cable 302 is functioningas expected, whereas a high DC resistance return path may indicate thepresence of a disconnect or other issue with the probe ground path.

In certain embodiments, the input ground 306 a and output ground 306 bmay be AC coupled, e.g., by way of an optional capacitor 310, to allowfor AC signal current flow during the check for a low DC resistancereturn path. Capacitor 310 may also be useful in reducing thehigh-frequency impedance of the probe ground path due to inductanceand/or resistance in the switch mechanism 308.

FIG. 4 illustrates an example of a third technique 400 for checking aground connection between an oscilloscope and a DUT, such as theoscilloscope 102 and the DUT 104 of FIG. 1, in accordance with certainembodiments of the disclosed technology. This example is similar to theexample illustrated in FIG. 3 in that it includes a probe or probe cable402 that has a signal input 404 a, e.g., to receive an active signalfrom the DUT, a signal output 404 b, e.g., to provide the signal to theoscilloscope, an input ground 406 a, e.g., to connect to the DUT ground,and an output ground 406 b, e.g., to connect to the oscilloscope ground.

The example illustrated in FIG. 4 is different from the exampleillustrated in FIG. 3, however, in that the technique 400 includes abuffer amplifier 408 and voltage source 410, e.g., a DAC, between theinput ground 406 a and the output ground 406 b rather than a switchmechanism separating the input ground 406 a from the output ground 406b. Here, the voltage source 410 can be programmed to drive the inputground [through the buffer amplifier 408] to 0.0 V, e.g. ground, fornormal operation or to some non-zero voltage to check for alow-impedance path back to the scope ground through the auxiliary path.That is, this technique can check for an output current-limit conditionin the buffer amplifier 408 to determine a low-resistance path.

The example illustrated in FIG. 4 also includes a capacitor 412 inparallel with the buffer amplifier 408 and voltage source 410. Bymonitoring the behavior, e.g., current draw, of the buffer amplifier 408and voltage source 410, a determination may be made as to whether thereis a disconnect or other issue with regard to the ground path within theprobe cable 402 or the connection to the DUT ground at 406 a.

The techniques 300 and 400 of FIGS. 3 and 4, respectively, providevarious advantages. For example, the physical implementations have thepotential of being very small. Also, the implementations of thesetechniques generally do not interfere with typical probe signal-pathdesigns. Further, probe ground path integrity verification can betypically performed without affecting active signal acquisitions, atleast in situations where the connection is solid.

FIG. 5 illustrates an example of a fourth technique 500 for checking aconnection between an oscilloscope probe and a DUT in accordance withcertain embodiments of the disclosed technology. The example includes aprobe or probe cable 502 that has a signal input 504 a, e.g., to receivean active signal from the DUT, a signal output 504 b, e.g., to providethe signal to the oscilloscope, an input ground 506 a, e.g., to connectto the DUT ground, and an output ground 506 b, e.g., to connect to theoscilloscope ground. In this example, however, there is no auxiliaryground connection so the technique involves checking the DUT signal andground connections as well as the DUT drive impedance.

The example further includes a resistor 508 and a voltage source 510such that the probe termination voltage may be adjusted. Once thevoltage has been adjusted, a check may be made as to whether thecalculated probe tip voltage stays relatively constant. A low-resistancedrive generally indicates good connections, whereas a high-resistancedrive generally indicates a bad connection, in which case the probe tipvoltage may track the termination voltage.

In situations involving a differential or TriMode™ probe, each pertinenttermination voltage may be adjusted. If the termination voltages of thedifferential or TriMode probe can be adjusted independently and/or theprobe tip voltages measured independently, the two probe tip connectionsmay be independently verified. Otherwise, a solid connection for bothprobe tips may still be simultaneously verified. Also, the differentialprobe tip signal connections can be verified with this techniqueindependent of the absence or presence of an auxiliary groundconnection.

Implementations of this technique 500 are particularly advantageous inthat they can be fully implemented as software for many existing probedesigns that provide adjustable termination voltages, so there is noneed for additional probe hardware to perform the ground checking.

FIG. 6 illustrates an example of a fifth technique 600 for checking aconnection between an oscilloscope probe and a DUT in accordance withcertain embodiments of the disclosed technology. The example includes aprobe or probe cable 604 configured to receive an input differentialsignal via DUT inputs 606 a and 608 a from DUT 602 and provide an outputdifferential signal 616, e.g., to an oscilloscope.

In the example, the output differential signal 616 is generated by wayof the input differential signal received from DUT inputs 606 a and 608a being passed to internal circuitry 614 via internal inputs 606 b and608 b. The probe 604 also includes resistors 610 a and 610 b and avoltage source 612 for adjusting the signal being passed to the internalcircuitry 614 via the internal inputs 606 b and 608 b. This technique600 is particularly advantageous in that it may be used to check for anintact differential connection, including differential ground path,regardless of whether an auxiliary ground connection 618 is present.

FIG. 7 illustrates an example of a sixth technique 700 for checking aground connection between a DUT 702 and an oscilloscope 704 inaccordance with certain embodiments of the disclosed technology. Theexample is similar to the example illustrated in FIG. 5 in that itincludes a probe or probe cable 706, e.g., a de-embed probe, that has asignal input 708 a, e.g., to receive an active signal from the DUT 702,a signal output 708 b, e.g., to provide the signal to the oscilloscope704, an input ground 710 a, e.g., to connect to the ground of the DUT702, and an output ground 710 b, e.g., to connect to the ground of theoscilloscope 704.

In the example, a sub-assembly including a switching mechanism 712 andtwo impedance elements 714 and 716, where impedance element 716represents the normal input impedance of the probe or probe cable 706,may be used to measure the source impedance driving the probe 706. Themeasured source impedance may then be compared with the expected sourceimpedance, e.g., as determined by knowledge of the DUT 702. Asubstantially similar or identical match of the source impedance withthe expected impedance generally indicates a good connection, whereas amismatch generally indicates a disconnect or other issue with regard tothe signal or ground connection between the DUT 702 and the probe orprobe cable 706.

Implementations of this technique 700 are particularly advantageous inthat, because they can be fully implemented as software, there is noneed for additional probe hardware to perform the ground checking.Further, this technique 700 may be used to check both signal and groundlead connections, because a bad ground connection will generally bereflected in high source impedance for at least certain frequency bands.

In certain embodiments, a communication may be issued based on thechecking of the probe ground connection using any of the techniquesdescribed herein. For example, an alert may be issued responsive to adetermination that a disconnect or other issue is or may be presentwithin the probe ground connection. In certain embodiments where no suchdisconnect or other issue is detected within the probe groundconnection, a notification may be issued to advise the user that theprobe ground connection appears to be solid.

An alert or notification such as those described above may include avisual indication, e.g., the lighting of an LED or issuing of atext-based or other type of message, an audible indication, e.g., abuzzing sound or other noise suitable to be heard by a user, or anysuitable combination thereof. Alternatively or in addition thereto, thealert or notification may be delivered to the user by way of the testmeasurement device itself, e.g., by way of an oscilloscope display.

Having described and illustrated the principles of the invention withreference to illustrated embodiments, it will be recognized that theillustrated embodiments may be modified in arrangement and detailwithout departing from such principles, and may be combined in anydesired manner. And although the foregoing discussion has focused onparticular embodiments, other configurations are contemplated.

In particular, even though expressions such as “according to anembodiment of the invention” or the like are used herein, these phrasesare meant to generally reference embodiment possibilities, and are notintended to limit the invention to particular embodiment configurations.As used herein, these terms may reference the same or differentembodiments that are combinable into other embodiments.

Consequently, in view of the wide variety of permutations to theembodiments described herein, this detailed description and accompanyingmaterial is intended to be illustrative only, and should not be taken aslimiting the scope of the invention. What is claimed as the invention,therefore, is all such modifications as may come within the scope andspirit of the following claims and equivalents thereto.

What is claimed is:
 1. A test system, comprising: a probe suitable to becoupled between a test measurement device and a device under test (DUT),said probe comprising: a signal input configured to electrically receivean active signal from the DUT; a signal output configured toelectrically provide the active signal to the test measurement device;an input ground configured to electrically connect to a ground of theDUT; and an output ground configured to electrically connect to a groundof the test measurement device; and a probe ground connection checkingdevice configured to automatically determine whether a suitable groundconnection exists between said probe input ground and said DUT ground.2. The test system of claim 1, wherein said test measurement devicecomprises an oscilloscope.
 3. The test system of claim 1, wherein saidprobe ground connection checking device is configured to determinewhether a sufficiently low impedance exists from said probe input groundthrough said DUT ground, an auxiliary ground connection from said DUTground to said test measurement device ground, and back to said probeoutput ground.
 4. The test system of claim 1, further comprising analert mechanism configured to provide a user with an alert responsive toa determination that there is no suitable ground connection between saidprobe input ground and said DUT ground.
 5. The test system of claim 1,further comprising a notification mechanism configured to provide a userwith a notification responsive to a determination that said suitableground connection between said probe input ground and said DUT groundexists.
 6. A probe ground connection checking device, comprising: amagnetic core configured to receive a probe cable therethrough; and atest coil configured to be coupled with said magnetic core and furtherconfigured to receive an alternating current such that an impedancethereof may be measured and used in determining whether a ground loopexists, said ground loop including a probe cable ground path andappropriate ground connections at both ends of said probe cable.
 7. Theprobe ground connection checking device of claim 6, wherein saidmagnetic core is permanently coupled to said probe cable.
 8. The probeground connection checking device of claim 7, wherein said test coil ispermanently coupled to said magnetic core.
 9. The probe groundconnection checking device of claim 6, wherein said magnetic core isremovably attachable to said probe cable.
 10. The probe groundconnection checking device of claim 6, further comprising an alertmechanism configured to provide a user with an alert responsive to adetermination that said ground loop does not exist.
 11. A probe groundconnection checking device, comprising: a probe having an input groundconfigured to electrically connect to a ground of a device under test(DUT), an output ground configured to electrically connect to a groundof a test measurement device, and a probe ground path electricallycoupled between said input ground and said output ground; and aswitching mechanism within said probe ground path having an openposition configured to prevent a flow of direct current through saidprobe ground path, wherein a determination may be made as to whethersaid input ground is appropriately connected to said DUT ground and saidoutput ground is appropriately connected to said test measurement deviceground based on a determination as to whether a low DC resistance returnpath external to said probe exists based on said flow of direct current.12. The probe ground connection checking device of claim 11, wherein adetermination may be made as to whether said ground connection(s) maynot be solid based on a determination as to whether a high DC resistancereturn path exists based on said flow of direct current.
 13. The probeground connection checking device of claim 12, further comprising analert mechanism configured to provide a user with an alert responsive tosaid determination that said probe ground connection(s) may not besolid.
 14. The probe ground connection checking device of claim 11,further comprising an alternating current (AC) coupling across saidswitching mechanism.
 15. A probe ground connection checking device,comprising: a probe having an input ground configured to electricallyconnect to a ground of a device under test (DUT), an output groundconfigured to electrically connect to a ground of a test measurementdevice, and a probe ground path electrically coupled between said inputground and said output ground; and a buffer amplifier disposed withinsaid probe ground path, wherein a determination may be made as towhether said input ground is appropriately connected to said DUT groundand said output ground is appropriately connected to said testmeasurement device ground based on a monitoring of the behavior of saidbuffer amplifier.
 16. The probe ground connection checking device ofclaim 15, further comprising an alert mechanism configured to provide auser with an alert responsive to a determination that said probe groundconnection(s) may not be solid.
 17. A connection checking device,comprising: a probe having at least two probe inputs configured toelectrically connect to respective input nodes of a device under test(DUT) and at least one adjustable termination voltage between the atleast two probe inputs; and a software application configured to adjustsaid termination voltage of said probe, check whether the voltage acrossthe at least two probe inputs remains at least substantially constantduring said adjusting, and determine whether the probe connection(s) aresolid based at least in part on said checking.
 18. The connectionchecking device of claim 17, further comprising an alert mechanismconfigured to provide a user with an alert responsive to a determinationthat said probe connection(s) may not be solid.
 19. The connectionchecking device of claim 17, wherein one of the at least probe inputs isan input ground configured to electrically connect to a ground of saidDUT.
 20. A connection checking device, comprising: a de-embed probeoperable to measure a source impedance driving said probe; and asoftware application configured to compare said measured sourceimpedance to an expected source impedance and determine whether at leastone probe connection is solid based on said comparing.
 21. Theconnection checking device of claim 20, further comprising an alertmechanism configured to provide a user with an alert responsive to adetermination that said at least one probe connection may not be solid.